The usual hydrotherapy machine includes a tank and a pumping system for inducing circulation of liquid within the tank. The particular liquid within the tank is usually prepared according to the needs of the treatment being administered. Usually, the liquid will be water with selected additives. Selected temperatures can usually be maintained by the use of a heater interposed in the plumbing system. A patient is usually seated near the edge of the tank, immersing whatever portion of his body is being subject to treatment. Larger machines are capable of receiving the whole body of a patient, somewhat in the manner of a bathtub. The fairly high velocity of circulation of liquid within the tank has the effect of stimulating the peripheral portions of the body and relaxing the interior muscles. Blood circulation can usually be increased in the areas around an injury, and solutions can be prepared that are appropriate for treating burns and other open skin lesions. The velocity of circulation is usually controllable as particular conditions on the patient's body may require. These machines also commonly include an air injection system that provides small entrained air bubbles, which seem to be beneficial in certain types of treatment. The addition of small quantities of detergent will sufficiently reduce the surface tension of the liquid to produce a smaller bubble size.
Conventional hydrotherapy machines produce the circulation within the tank with the use of transverse jets emerging from nozzles in various locations. Usually the directional orientation of these jets is horizontal, producing undesirable impact areas that can produce discomfort and possible damage to sensitive areas on the body. The use of jets also tends to produce stagnant areas in the tank, and correspondingly wide fluctuations in the velocity of circulation at various points where the patient's body may be immersed.